Enabling Coexistence of High-Density and Low-Density Transmissions

ABSTRACT

Embodiments may comprise logic such as hardware and/or code to enable coexistence of high-density and low-density transmissions with a modified CSMA protocol. Embodiments include a self-CTS (self clear to send) packet transmission prior to transmission of a ready to send (RTS) signal when initiating a high density transmission amidst legacy devices. In many embodiments, the self-CTS or the RTS includes a network allocation vector (NAV) having a value for the duration of the transmission. In some embodiments, the self-CTS may include a flag or bit to indicate the Shading Transmission Starts (STS).

BACKGROUND

The present disclosure relates generally to wireless communicationstechnologies. More particularly, the present disclosure relates toenabling coexistence of high-density and low-density transmissions.

Wireless capability allows a variety of devices to communicate with eachother adding to the mobility of users. A computing device, such as aPersonal Computer (PC), may be used with various peripherals that arenot wired together, but rather communicate using wirelesscommunications, such as Wireless Local Area Network (WLAN) typeprotocols.

The density of the future distributed systems such as WiFi™ keepsgrowing. One very relevant example is that Intel is trying to ramp updensity of wireless displays (WiDi). Wireless display (WiDi) is atechnology in which image information, such as video information andaudio information, on a computer display/screen is captured and encoded,and is then wirelessly transmitted to an adapter. For example, the videoinformation and audio information may be wirelessly transmitted throughWiFi™, which is a superset of the standards of IEEE 802.11 for a WLANprotocols. The video data is then decoded and displayed on anotherscreen, such as a screen on a high definition television (HDTV) and theaudio may be decoded and sounded through speakers for the HDTV. Thequality of the video and audio expressed by the HDTV is dependent uponthe throughput of the wireless channel for transmitting the encodedvideo and audio data. The throughput of the wireless channel isdependent upon channel conditions, such as the signal to noise ratio(SNR), which may detrimentally change to adversely affect video qualityon the display screen and/or the audio quality sounded by the speakers.

It is well-known that using excessive power, e.g. 17 dBm (decibelsrelative to one milliwatt), is unnecessary and actually lowers systemperformance significantly due to interference with reception of paralleltransmissions. For example, a 17 dBm plus 3 dBi (decibel isotropic)antenna has an interference radius of about 40 to 50 meters, while zerodBm is enough to provide 30 dB SNR at a distance of five meters.Shrinking from full power for transmissions to a power level that isnecessary could achieve five times more transmissions.

Yet, not many devices are lowering power due to the fact that the actonly benefits other devices and not necessarily the devices thatactually lower the power for transmissions. Lowering the power fortransmission may even interfere with ability of a receiving device toreceive the transmission when there are legacy devices nearby. Thereceiving device may have difficulty receiving the lower powertransmission because of the asymmetric interference footprint betweenthe high power or excessive power transmissions from legacy devices andthe low power transmissions. The low power link established for the lowpower transmissions may not be able reach the legacy devices but thehigh power transmissions from a high power link can reach the low powerdevices and destroy the well-known CSMA-based RTS/CTS/DATA/ACK handshakefor preventing hidden nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a system to enable the coexistence ofhigh-density and low density transmissions;

FIG. 2 depicts an embodiment of an apparatus to enable the coexistenceof high-density and low density transmissions;

FIG. 3 depicts an embodiment of a timing and power diagram to enable thecoexistence of high-density and low density transmissions;

FIG. 4 depicts an embodiment of a timing and power diagram to enable thecoexistence of high-density and low density transmissions; and

FIG. 5 illustrates a flow chart of another embodiment to initiate andjoin high-density transmissions.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of novel embodiments depicted inthe accompanying drawings. However, the amount of detail offered is notintended to limit anticipated variations of the described embodiments;on the contrary, the claims and detailed description are to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the present teachings as defined by the appended claims.The detailed descriptions below are designed to make such embodimentsunderstandable to a person having ordinary skill in the art.

Wireless personal area network (WPAN) protocols and devices enablemobility and flexibility in computing systems, where devices andcomponents may be implemented using wireless technology. For example, apersonal computer (PC) may include a wireless processing unit, awireless keyboard, a wireless mouse, and a wireless display. The PC thensends wireless signals to a display or other unit that contains awireless adapter for receiving wireless signal, thus reducing the wiredconnections of a system. A system using, for example, WPAN 802.11a/b/g/n protocol signaling, enables hundreds of Megabits of wirelesscommunications over a local area network (LAN) using Orthogonalfrequency-division multiplexing (OFDM) technology.

Wireless devices that use the 802.11b/g/n protocol may use the 2.4Gigahertz (GHz) license free band and may occasionally sufferinterference from other devices and appliances utilizing 2.4 GHz signalssuch as microwave ovens, cordless telephones and Bluetooth devices.Network resources may also be shared with other 802.11 b/g/n wirelessdevices and applications and may therefore cause co-channel and adjacentchannel interference. The quality of the received wireless signal isstrongly dependent on the channel condition, which is in turn dependenton the sharing of channel resources with other wireless devices andapplications.

Carrier Sense Multiple Access (CSMA) is a probabilistic Media AccessControl (MAC) protocol in which a node verifies the absence of othertraffic before transmitting on a shared transmission medium, such as anelectrical bus, or a band of the electromagnetic spectrum. “CarrierSense” describes the fact that a transmitter uses feedback from areceiver that detects a carrier wave before trying to send. That is, ittries to detect the presence of an encoded signal from another stationbefore attempting to transmit. If a carrier is sensed, the station waitsfor the transmission in progress to finish before initiating its owntransmission. “Multiple Access” describes the fact that multiplestations send and receive on the medium. Transmissions by one node aregenerally received by all other stations using the medium.

CMSA is implemented by legacy devices. Embodiments generally build uponthe CMSA protocol to maintain compatibility with the legacy deviceswhile providing the low power devices a fair scheme for utilizing themedium to transmit data to receiving devices. For instance, embodimentsmay include wireless display (WiDi) devices wherein the transmitter istypically located near the receiver and can significantly reducetransmission power below the maximum rated power without sacrificingbandwidth.

Generally, wireless technologies for enabling the coexistence ofhigh-density and low-density transmissions are described herein.Embodiments may comprise logic such as hardware and/or code to enablecoexistence of high-density and low-density transmissions with amodified CSMA protocol. Embodiments include a self-CTS (self clear tosend) packet transmission prior to transmission of a ready to send (RTS)signal when initiating a high density transmission amidst legacydevices. In many embodiments, the self-CTS or the RTS includes a networkallocation vector (NAV) having a value for the duration of thetransmission. NAV is a virtual carrier sensing mechanism used withwireless network protocols such as IEEE 802.11 and IEEE 802.16 (WiMax).The virtual carrier sensing is a logical abstraction that limits theneed for physical carrier sensing at the air interface in order to savepower. The MAC layer frame headers contain a Duration field thatspecifies the transmission time required for the frame, in which timethe medium will be busy. The stations listening on the wireless mediumread the Duration field and set their NAV, which is an indicator for astation on how long that station must defer from accessing the medium.

Handshake packets (self-CTS, CTS, and RTS) carry NAVs that hold thechannel clear for the time stated in the NAV. A NAV covering up to theend of the ACK of the data packet are exchanged in the handshakepackets. The acknowledgement (ACK) at the end of the transmission has aNAV of zero to signal the immediate end of the transmission. Forinstance, a WiDi transmitter may, in an effort to initiate a low powertransmission, transmit a self-CTS with a NAV indicating a length of thetransmission. The WiDi transmitter may thereafter transmit an RTS andthe WiDi adapter that is the target of the transmission may transmit aCTS. The entire transmission from the transmission of the self-CTSthrough the end of the acknowledgement (ACK) package may be referred toas a “Shading Transmission” for the purposes of this disclosure. In someembodiments, the self-CTS may include a special address or flag bit toindicate that a “Shading Transmission Starts” (STS).

In several embodiments, the self-CTS and RTS issued by the WiDitransmitter and the CTS issued by the WiDi adapter may be transmitted atfull power or a higher power than is determined to be necessary for thedata transmission. The handshake packets (self-CTS, RTS, and CTS) may befollowed by an opportunity window for other low power transmitters tojoin the data period to transmit data in parallel with the WiDitransmitter to execute the shading transmission. The opportunity windowmay comprise a fixed period of time in some embodiments, during whichadditional wireless devices may join the shading transmission toschedule data transmissions during the data period of the shadingtransmission. The fixed opportunity window may be part of the protocolor may be a default time frame. In other embodiments, the opportunitywindow may be established by the handshake packets. For instance, themodulation/coding schemes (MCSs) of the self-CTS/RTS/CTS can be used tospecify the length of the opportunity window.

In many embodiments, additional transmitters may participate in the lowpower transmission by verifying the availability to join thetransmission and transmitting an RTS. In particular, a second device mayjoin the low power transmission if the second device is not beingblocked by another, e.g., legacy or low power device and if the joiningmay not interfere with a previously established transmission. Suchembodiments may determine whether the transmission power necessary formeeting a quality of service (QoS) will interfere with a previouslyscheduled transmission by a nearby device.

In further embodiments, devices that join a shading transmission mayissue a self-CTS. In some of these embodiments, issuing a self-CTS by atransmitter that joins the shading transmission may facilitate theinclusion of additional devices that were outside the transmission rangeof the originating device. For example, device A may initiate a shadingtransmission. Device C may recognize the Shading Transmission Start(STS) transmitted by device A and transmit a self-CTS and an RTS. DeviceD may respond with a CTS. Device E may be outside the transmission rangeof device A but may be within the transmission range of device C and mayrecognize the shading transmission that device C joined based upon oneor more of the handshake protocols between devices C and D. As a result,device E may also join the shading transmission. The shadingtransmission that device E perceives may have a shorter opportunitywindow. In some embodiments, device E identifies the shorter opportunitywindow based upon the remaining duration for the transmission indicatedby a NAV from device C. In other embodiments, the shorter opportunitywindow may be otherwise communicated in the handshake packets.

In some embodiments, the opportunity window may have a fixed period oftime after each self-CTS/RTS/CTS that is used to indicate the beginningof an opportunity window.

The device that detects multiple self-CTS/RTS/CTS patterns may use theearliest detected pattern within a fixed trace back window counted fromthe latest detected pattern for determining the effective opportunitywindow. In the previous example, since device E is outside the range ofdevice A, device E may not cause significant interference to thedestination of device A. Therefore, the opportunity window of device Emay not be shortened for device A. However, if device E is within therange of device A. Then device E detects the calls for opportunitywindows from device A first and then device C. In this case, device Emay to back trace the earlier self-CTS/RTS/CTS initiated by device Aafter it detects the self-CTS/RTS/CTS initiated by device C. Theeffective opportunity window is then set by the earliest call in thetrace back window, which is the self-CTS/RTS/CTS initiated by device A.The trace back window may be on the order of 100 micro seconds.

The data portion of the shading transmission may be transmitted at a lowpower level. The low power level may be predetermined or may bedetermined based upon a QoS requirement for the data transmission asdetermined by each transmitter individually.

Embodiments may use the 802.11 wireless local area network (WLAN)protocol including 802.11 a/b/g/n and 802.11AC with OFDM technology ateither a 2.4 GHz or 5 GHz band or 802.11AD at a 60 GHz band, or the802.11AD wireless personal area network (WPAN) protocol including, forexample, Ultra Wide Band (UWB) or Bluetooth® (BT), etc. as would berecognized by one skilled in the art.

While some of the specific embodiments described below will referencethe embodiments with specific configurations, those of skill in the artwill realize that embodiments of the present disclosure mayadvantageously be implemented with other configurations with similarissues or problems.

Turning now to FIG. 1A, there is shown an embodiment of a system at afirst moment in time, system state 100. System state 100 illustratesinteractions of transmissions from low power capable transmitters (110,120, 140, and 150) and legacy transmitters (130 and 160) along with thereceivers to which the transmitters are transmitting or intend totransmit data demarked by a line between the transmitter and receiverpairs. FIG. 1B shows the same system at a different moment in time,system state 180. The configuration and layout of the transmitters andreceivers is chosen for illustration purposes. Embodiments encompass anyconfiguration and layout of transmitters and receivers. In someembodiments, each self-CTS, RTS and CTS frames may comprise of onelegacy 802.11a/b/g frame sent by one antenna or may comprise one legacy802.11a/b/g frame sent by one antenna and/or one 802.11n frame sent bymultiple antennas.

System state 100 in FIG. 1A illustrates an instance in time at which twolegacy transmitters, 130 and 160, are transmitting data to theirrespective receivers. The volume of coverage for transmitter 130 bytransmission 132 is illustrated as a two dimensional area in which thetransmission 132 from transmitter 130 will interfere with reception by areceiver and the volume of coverage for transmitter 160 by transmission162 is illustrated as a two dimensional area in which the transmission162 from transmitter 160 will interfere with reception by a receiver.Note that the illustrated transmissions 132 and 162 theoretically formspherical patterns so the distances between the transmitters may residealong any axis. In other embodiments, transmitters may directtransmissions toward the intended receiver. Such embodiments have avolume of interference with a different pattern but, otherwise, the sameinteractions apply.

At system state 100, the transmission patterns from the legacytransmitters 130 and 160 prevent additional parallel transmissionsamongst the other transmitters (110, 120, 140, and 150) due tointerference with reception and WiFi™ protocols. For instance,transmitter 130 may transmit an RTS and may receive a CTS from thecorresponding receiver. The RTS and CTS may include NAV durations toreserve the transmission medium for the duration of the transmission orthe data period of the transmission may start after the CTS. Thetransmitters (110, 120, 140, and 150) may recognize that the medium isnot idle by the NAV or the initiation of the transmission by the legacytransmitter 130. Based upon the power of the transmission of the RTSand/or CTS, the transmitters (110, 120, 140, and 150) may determine thatthe communication between transmitter 130 and its receiver willinterfere with receipt of transmissions from transmitters (110, 120,140, and 150) by their respective receivers. Thus, the initiation of thetransmission by legacy transmitter 130 effectively blocks transmissionsby transmitters (110, 120, 140, and 150).

The legacy transmitter 160 and its receiver are not within theinterference area 132 so the legacy transmitter 160 may initiate aparallel transmission in the same manner as legacy transmitter 130. Notethat in this situation, transmitter 150 and its receiver are blocked bythe transmission initiated by transmitter 160 also.

At system state 180, there is shown the initiation of a low power, highdensity transmission. Transmission 112A illustrates the coverage of thetransmission of a self-CTS packet and an RTS packet from transmitter110. The transmission of the self-CTS packet indicates the beginning ofa shading transmission. In some embodiments, the self-CTS packet mayalso include a flag or bit to indicate that the Shading TransmissionStarts (STS). The receiver of transmitter 110 may then transmit a CTS,which is followed by an opportunity window for other transmitters tojoin. Transmitters (110, 120, 140, and 150) may recognize the initiationof a shading transmission based upon the transmission of the self-CTS, acombination of the self-CTS and RTS from transmitter 110, a combinationof the self-CTS and RTS from transmitter 110 and the CTS from thereceiver of transmitter 110, or the inclusion of the flag or bitindicative of the STS in the self-CTS.

One or more of the low power capable transmitters 130, 120, 140, and 150may join the shading transmission if they are not otherwise blocked. Inparticular, transmitter 120 may receive the NAV and store the NAV fromthe self-CTS, RTS, and CTS. Transmitter 120 may receive the self-CTS,RTS, and CTS and determine that the receiver for transmitter 110 issufficiently close to the transmitter 120 that a transmission fromtransmitter 120 would interfere with reception of the data transmission112B from transmitter 110 to its receiver. Thus, transmitter 120 maydetermine that the transmission 112A of the self-CTS from transmitter110 effectively blocks transmissions from transmitter 120 until the NAVexpires.

Similarly, the legacy transmitter 130 may receive the self-CTS, RTS, andCTS and determine that the receiver for transmitter 110 is sufficientlyclose to the legacy transmitter 130 that a transmission 132 fromtransmitter 130 would interfere with reception of the data transmission112B from transmitter 110 to its receiver. Thus, transmitter 130 maydetermine that the transmission 112B scheduled for the transmitter 110effectively blocks transmissions from transmitter 130 until the NAVexpires.

Transmitter 140 may receive the self-CTS, RTS, and CTS. In response,transmitter 140 may determine that the transmission power thattransmitter 140 must emit to meet the QoS requirements for transmittingdata to its receiver will be less than the transmission power estimatedto interfere with the data transmission 112B from the transmitter 110 toits receiver during the data period of the shading transmission. Inresponse, transmitter 140 may transmit a CTS and the receiver oftransmitter 140 may respond with an RTS during the opportunity window ofthe shading transmission.

Transmitter 150 may receive the self-CTS, RTS, and CTS. If transmitter150 receives a NAV from transmitter 160 after receiving the NAV fromtransmitter 110 and prior to having the opportunity to join the shadingtransmission, transmitter 150 would be blocked from joining the shadingtransmission. On the other hand, if transmitter 160 did not issue a NAV,transmitter 150 may determine that the transmission power thattransmitter 150 must emit to meet the QoS requirements for transmittingdata to its receiver will be less than the transmission power estimatedto interfere with the data transmission 112B from the transmitter 110 toits receiver during the data period of the shading transmission. Inresponse, transmitter 150 may transmit an RTS and the receiver oftransmitter 150 may respond with a CTS during the opportunity window ofthe shading transmission. Furthermore, the CTS issued by the transmitter150 may block transmitter 160 from transmitting over the medium untilthe NAV that transmitter 160 receives from transmitter 150 expires.

Turning now to FIG. 2, there is shown an embodiment of a system 200. Thesystem 200 may, for example, include a computing device 205, which mayinclude a processor 202 and a memory 204 as shown. In some embodiments,the processor 202 and the memory 204 may comprise hardware generallyused by the computing device 205. In further embodiments, the processor202 and the memory 204 may comprise hardware attached to an adapter cardsuch as an adapter card for a transmitter. In some embodiments, thecomputing device 205 may include a desktop computer, personal computer,workstation, server, or a portable wireless communication device, suchas a notebook, laptop, Netbook, smart phone, personal digital assistant(PDA), a web tablet, a wireless telephone, an instant messaging device,a digital camera, an access point, a television, a medical device (e.g.,a heart rate monitor, a blood pressure monitor, etc.), or other devicethat may receive and/or transmit information wirelessly.

The computing device 205 may comprise a video encoder/audio encoder 212,and a WiFi™ transmitter 215. The video encoder/audio encoder 212 mayencoder video data and audio data for transmission across wirelesschannel 225 to WiDi adapter 235.

The WiFi™ transmitter 215 may transmit the compressed video and audiodata from the video encoder/audio encoder 212 via an antenna 220 throughan interface protocol by way of a wireless channel 225 and may sendinformation such as video data, packet information, physical data rate,number of passing packets, number of failing packets, etc., to theprocessor 202. The interface protocol may include a local area network(LAN) 802.11 a/b/g/n, 802.11 AC and 802.11AD protocol, or a personalarea network (PAN) protocol such as, for example, ultra wide band (UWB),Bluetooth® (BT), or the like. The WiFi receiver 230 of a WiDi (wirelessdisplay) adapter 235 may receive the compressed video and audio signalby way of an antenna 240. The WiFi™ receiver 230 may send the receivedcompressed video and audio data to a video decoder/audio decoder 232 forvideo decompression and audio decompression, after which thedecompressed video data and audio data may be sent to a display devicesuch as HDTV 250 using an interface protocol such as High-DefinitionMultimedia Interface (HDMI) via an HDMI cable 245. Other embodiments mayuse other interface protocols such as a Mobile Industry ProcessorInterface (MIPI) Display Serial Interface (DSI), regardless of thecontent of the display data. Thus, both the computing device 205 and theWiDi adapter 235 may support wireless communications. Although notshown, embodiments also encompass integrating the WiDi adapter 235 intothe TV to save an HDMI wired connection, or to have a wirelessconnection between the adapter and the TV.

In some embodiments, the WiFi™ transmitter 215 may be configured totransmit Orthogonal Frequency-Division Multiplex (OFDM) communicationsignals over a multicarrier communication channel. The OFDM signals maycomprise a plurality of orthogonal subcarriers. In some of thesemulticarrier embodiments, the WiFi™ transmitter 215 may be part of aWireless Local Area Networks (WLANs) communication station such as aWireless Access Point (WAP), base station or a mobile device including aWireless-Fidelity (Wi-Fi) device. In some other embodiments, the WiFi™transmitter 215 may be configured to transmit signals that weretransmitted using one or more other modulation techniques such as spreadspectrum modulation (e.g., Direct Sequence Code Division-Multiple Access(DS-CDMA) and/or Frequency Hopping Code Division-Multiple Access(FH-CDMA)), Time Division-Multiplexing (TDM) modulation, and/orFrequency Division-Multiplexing (FDM) modulation, although the scope ofthe embodiments is not limited in this respect.

The WiFi™ transmitter 215 may comprise a WiFi™ transmit control 217 tofacilitate adjustment of the power level of a transmission. Forinstance, in the present embodiment, the WiFi™ transmitter 215 maytransmit handshake packets such as self-CTS and RTS at a first powerlevel such as full power for the transmitter (e.g. 17 dB). The WiFi™transmitter 215 may, via WiFi™ transmit control 217, be capable oftransmitting packets at other power levels such as transmitting a datatransmission at a minimum power level to provide QoS (e.g. 0 dBm) forthe WiDi adapter 235.

Antennas 220 and 240 may comprise one or more directional oromni-directional antennas, including, for example, dipole antennas,monopole antennas, patch antennas, loop antennas, micro-strip antennasor other types of antennas suitable for transmission of RF signals.

As further seen in FIG. 2, the memory 204 may store logic 206 andbuffers such as a NAV buffer 208 and a NAV Device buffer 209. The logic206 may comprise processing instructions in the form of a WiFi™ driver207, a distance estimator 210, and a power level determiner 211. Inother embodiments, one or more or all of these items in logic 206 andthe buffers of memory 204 may be incorporated into hardware such as aspecial purpose processor, a state machine, or the like. In furtherembodiments, the logic 206 may reside on a transmitter adapter card inthe form of code and/or hardware.

The WiFi™ driver 207 may be configured to direct the processor 202 todetermine the transmission power level (p1) to support the quality ofservice (QoS) for the WiFi™ receiver 230 of the WiDi adapter 235. Insome embodiments, the WiFi™ driver 207 may determine a current datatransmission rate capacity of the wireless channel 225 to determine thetransmission power level (p1).

The NAV buffer 208 may store one or more NAV values and the NAV devicebuffer 209 may store an indication of the transmitter responsible forthe one or more NAV values. For example, the WiFi™ driver 207 maydetermine whether the NAV value is from a NAV device that blocks theWiFi™ transmitter 215 from initiating or joining a shading transmission.In particular, the WiFi™ driver 207 may determine if a NAV value isassociated with another low power capable device. If so, the WiFi™transmitter 215 may be able to join the shading transmission so that theWiFi™ transmitter 215 can transmit data to the WiFi™ receiver 230 duringthe data period of the shading transmission and in parallel with otherdata transmissions.

In some embodiments, two NAV counter(s) 213 may be employed, one for lowpower capable devices and the other for low power incapable devices. Ifthe NAV counter 213 of low power incapable device decreases to zero,then the device is not blocked by legacy devices incapable of low powertransmission and may be able to join or initiate a shading transmission.If both the NAV counter(s) 213 of the low power capable and the lowpower incapable decrease to zeros, then the device can initiate ashading transmission. If the NAV counter 213 of the low power incapableis zero but the NAV counter 213 of the low power capable is not zero,then the device may determine the effective opportunity window forjoining the shading transmission initiated by another device low powercapable. If there is still time left in the effective opportunitywindow, the device may estimate the interference level at each alreadyscheduled receivers known by the device for determining if it shouldcontend for a low power transmission in the remaining window. Fordetermining the effective opportunity window, a buffer of NAV and theirassociated starting time may be needed and may be implemented in NAVbuffer 208. The NAV buffer 208 may contain NAVs and their starting timewithin a predetermined trace back window. The low power capable NAV maybe detected from the pattern of self-CTS/RTS/CTS or some flag bit in theself-CTS/RTS/CTS handshake exchange.

The WiFi™ driver 207 may also determine if the NAV value is associatedwith a NAV device that is not capable of a low power transmission suchas a legacy device. If so, the WiFi™ transmitter 215 may not join thetransmission and may be blocked from initiating another transmission onthe medium until the transmission terminates.

The distance estimator 210 may estimate a distance from a transmitterand a distance from a receiver based upon handshake packets receivedfrom the transmitter and receiver. Based upon these distances, powerlevel determiner 211 may determine a power level (p2) at which a datatransmission from the WiFi™ transmitter 215 may interfere with receptionof a data transmission by the receiver. For example, a first transmittermay establish a shading transmission to transmit data to a firstreceiver. The WiFi™ transmitter 215 may first check to see if anothertransmission blocks the WiFi™ transmitter 215 from joining the shadingtransmission. If the WiFi™ transmitter 215 is not blocked from joiningthe shading transmission, the WiFi™ transmitter 215 determines two powerlevels: the power level p1 to support QoS to

WiFi™ receiver 230 and the power level p2 that is a power levelsufficiently low to avoid interfering with reception of a datatransmission by the first receiver from the first transmitter. Thispower level may be predetermined based upon the distance from the firstreceiver to the WiFi™ transmitter 215. In some embodiments, this powerlevel may be estimated based upon the power drop of the CTS packetreceived from the first receiver. For example, −80 dBm may be assumed tobe a power level at which the transmission does not interfere withreception of another transmission.

In many embodiments, a distance between the first receiver and the firsttransmitter may be assumed in the estimation of the power sufficient tointerfere with the reception. If the power level p2 is greater than thepower level p1, the WiFi™ transmitter 215 will use the power level p1 totransmit during the data period of the shading transmission. On theother hand, if the power level p2 is less than the power level p1, theWiFi™ transmitter 215 will be effectively blocked from transmitting overthe medium until the shading transmission has ended.

FIG. 3 illustrates an embodiment of a timing and power diagram to enablethe coexistence of high-density and low density transmissions for asystem such as the system 100 shown in FIG. 1. The timing and powerdiagram illustrates the initiation of a shading transmission 350 bytransmitter A and receiver B demarked by AB 310. The diagram alsoillustrates the joining of the shading transmission by transmitter C andreceiver D demarked by CD 330. Note that time progresses from left toright and power is indicated roughly by the height of the items within arow, i.e., the rows of AB 310 and CD 330. Note also that any number oftransmitters and receivers may join the shading transmission so long asthey determine that they will not interfere with reception by the otherreceivers in the shading transmission 350, the transmitters andreceivers are not blocked by another scheduled transmission, and thereis time within the opportunity window to join the shading transmission350. Note also that the heights of the handshake packets (self-CTS 312,RTS 314, CTS 316) and the data 320 are representative of the relativepower levels at which they are transmitted.

Transmitter A transmits the self-CTS 312 followed shortly thereafter byan RTS 314. The self-CTS 312 and the RTS 314 may include NAV valuesindicative of the duration of the shading transmission that thetransmitter A is initiating. Receiver B may respond to the self-CTS 312and the RTS 314 with a CTS 316. In the present embodiment, transmitter Aand receiver B may transmit the handshake packets at full power tonotify nearby legacy devices that the medium is busy for the durationindicated by the NAV.

The shading transmission 350 includes an opportunity window 318established by AB 310. The opportunity window 318 allows other low powercapable devices to join the shading transmission to transmit data inparallel with AB 310 during the data period 320. AB 310 does nottransmit during the opportunity window 318 as indicated by the dashedlines. The ACK 322 terminates the shading transmission 350. Note thatthe data period 320 includes the low power transmission. The low powerutilized by AB 310 is determined based upon the QoS required for thetransmission. Note also that in other embodiments, the ACK 322 may betransmitted at a higher power level than the data transmission.

CD 330 represents the timing and power diagram of the transmissions fromtransmitter C to receiver D. Transmitter C may recognize the shadingtransmission initiated by AB 310 based upon one or more of the handshakepackets. CD 330 may determine if CD 330 is blocked from using the mediumby another device such as a legacy transmitter or another low powercapable transmitter that is outside the range of AB 310 but withintransmission range of CD 330. CD 330 may determine if it is blocked bychecking the NAV and the device associated with the NAV.

CD 330 may then determine whether the joining the shading transmission350 will interfere with the reception of the data transmission fromtransmitter A to receiver B during the data period 320. Note that if asubsequent transmitter and receiver joins, the subsequent transmitterwould have to determine a transmission power level that would notinterfere with AB 310 and that would not interfere with CD 330. If CD330 determines a power level that both satisfies a QoS for the datatransmission of CD 330 during the data period, transmitter C transmits aRTS 332 at the beginning of opportunity window 318 and receiver Dresponds with a CTS 334. Transmitter C then waits for the remainingduration of the opportunity window 318, which is depicted as theopportunity window 336, before transmitting data during the data period338 and the ACK 340. Note that the data transmission of data period 338is performed at the same time as or partially overlap with the datatransmission of the data period 320, which can be seen by the relativepositioning of the data periods 320 and 338 with respect to one another.

FIG. 4 depicts an embodiment of a timing and power diagram to enable thecoexistence of high-density and low density transmissions. The contentof FIG. 4 is the same as FIG. 3 in most respects to illustrate adifferent protocol for CD joining the shading transmission initiated byAB. In particular, transmitter C first issues a self-CTS 410 and then anRTS before receiver D transmits a CTS. This additional self-CTS 410 mayprovide notice to other receivers beyond the transmission range oftransmitter A that the shading transmission can be joined. In suchsituations, the self-CTS 410, RTS, and/or CTS may communicate theremaining duration of the opportunity window. For example, themodulation/coding schemes (MCSs) or some bit flag of theself-CTS/RTS/CTS can be used to specify the length of the opportunitywindow.

Furthermore, the self-CTS 410 may include a flag or bit to indicate theshading transmission starts. In other embodiments, the self-CTS 410 maydistinguish the transmission from a legacy transmission and potentiallyother variants of the shading transmission that are implemented innearby devices.

FIG. 5 illustrates an embodiment of a flow chart 500 to enhanceperformance of a wireless display transmission for a system such as thesystem 200 illustrated in FIG. 2. The flow chart 500 begins withdetermining, by a first transmitter, whether a value of a networkallocation vector maintained by the first transmitter indicates that thefirst transmitter is blocked from transmitting on a medium at element510. If the first transmitter is blocked, the first transmitter willwait until the blocking transmission completes. If the first transmitteris not blocked, the first transmitter may be available to initiate ashading transmission or to join a shading transmission.

If the first transmitter is determining whether to join a shadingtransmission. The first transmitter will continue with the element 520.Otherwise, the flow chart 500 skips to element 530. The element 520involves determining whether transmitting data at the second power levelmay interfere with reception of a second data transmission. In otherwords, before joining a shading transmission, the first transmittershould determine whether joining the transmission will causeinterference more than an acceptable amount of interference with otherdevices that are already joined in the shading transmission. In someembodiments, determining whether transmitting data at the second powerlevel may interfere with reception of a second data transmissioninvolves estimating a distance between a second receiver and the firsttransmitter based upon a drop in power from a ready to send packettransmitted by the second receiver. In further embodiments, determiningwhether transmitting data at the second power level may interfere withreception of a second data transmission involves estimating a powerattenuation between a second receiver and the first transmitter basedupon a drop in power from a ready to send packet transmitted by thesecond receiver.

In several embodiments, determining whether transmitting data at thesecond power level may interfere with reception of a second datatransmission comprises estimating a third power level that is a powerlevel to transmit the first data transmission that avoids interferingwith the second data transmission. In such embodiments, estimating athird power level that is a power level to transmit the first datatransmission that avoids interfering with the second data transmissionmay involve estimating the third power level as the maximum power levelfor transmitting the first data transmission that avoids interferingwith the second data transmission.

In the present embodiment, an optional element for joining a shadingtransmission involves transmitting, by the first transmitter, a firstCTS packet at a first power level in response to determining that thefirst transmitter is not blocked from transmitting on the medium atelement 530. The CTS may comprise a self-CTS and, in some embodiments,the self-CTS may include a flag or bit to indicate that the shadingtransmission starts. In many embodiments, the first power level is afull power level.

Thereafter, the first transmitter may transmit a first RTS packet at afirst power level in response to determining that the first transmitteris not blocked from transmitting on the medium at element 540. And thefirst transmitter may receive a second clear to send packet at element550.

Once the handshake packets have been transmitted, the first transmittermay wait for an opportunity window time period to expire at element 560.The opportunity window time period is a time period during which otherlow power capable devices may join the shading transmission.

The first transmitter may then transmit a first data transmission at asecond power level, the second power level being less than the firstpower level at element 570. In many embodiments, transmitting, by thefirst transmitter, the first data transmission at the second power levelinvolves transmitting the first data transmission at a fourth powerlevel determined to provide quality of service for the first datatransmission by the first transmitter. In some embodiments, transmittingthe first data transmission at a fourth power level determined toprovide quality of service for the first data transmission by the firsttransmitter involves transmitting the first data transmission at thefourth power level, wherein the fourth power level is a minimum powerlevel that supports a quality of service for the first datatransmission.

Another embodiment is implemented as a program product for implementingsystems and methods described with reference to FIGS. 1-5. Embodimentscan take the form of an entirely hardware embodiment, an entirelysoftware embodiment, or an embodiment containing both hardware andsoftware elements. One embodiment is implemented in software, whichincludes but is not limited to firmware, resident software, microcode,etc.

Furthermore, embodiments can take the form of a computer program productaccessible from a computer-usable or computer-readable medium providingprogram code for use by or in connection with a computer or anyinstruction execution system. For the purposes of this description, acomputer-usable or computer readable medium can be any apparatus thatcan contain, store, communicate, propagate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device.

Note that a tangible storage medium does not store signals but storesone or more values representative of data. A medium can be anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system (or apparatus or device) or a propagation medium.Examples of a computer-readable storage medium include tangible mediasuch as semiconductor or solid-state memory, magnetic tape, a removablecomputer diskette, a random access memory (RAM), a read-only memory(ROM), a rigid magnetic disk, and an optical disk. Current examples ofoptical disks include compact disk—read only memory (CD-ROM), compactdisk—read/write (CD-R/W), and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the system eitherdirectly or through intervening I/O controllers. Network adapters mayalso be coupled to the system to enable the data processing system tobecome coupled to other data processing systems or remote printers orstorage devices through intervening private or public networks. Modems,cable modem, and Ethernet adapter cards are just a few of the currentlyavailable types of network adapters.

The logic as described above may be part of the design for an integratedcircuit chip. The chip design is created in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips, the designer transmitsthe resulting design by physical means (e.g., by providing a copy of thestorage medium storing the design) or electronically (e.g., through the

Internet) to such entities, directly or indirectly. The stored design isthen converted into the appropriate format (e.g., GDSII) for thefabrication of photolithographic masks, which typically include multiplecopies of the chip design in question that are to be formed on a wafer.The photolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

The resulting integrated circuit chips can be distributed by thefabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It will be apparent to those skilled in the art having the benefit ofthis disclosure that the present disclosure contemplates coexistence ofhigh and low density transmissions. It is understood that the form ofthe embodiments shown and described in the detailed description and thedrawings are to be taken merely as examples. It is intended that thefollowing claims be interpreted broadly to embrace all variations of theexample embodiments disclosed.

1. A method to enable coexistence of high-density and low-densitytransmissions on a medium, the method comprising: determining, by afirst transmitter, whether a value of a network allocation vectormaintained by the first transmitter indicates that the first transmitteris blocked from transmitting on a medium; transmitting, by the firsttransmitter, a first ready to send packet at a first power level inresponse to determining that the first transmitter is not blocked fromtransmitting on the medium; receiving, by the first transmitter, asecond clear to send packet; and transmitting, by the first transmitter,a first data transmission at a second power level, the second powerlevel being less than the first power level.
 2. The method of claim 1,further comprising transmitting, by the first transmitter, a first clearto send packet at a first power level in response to determining thatthe first transmitter is not blocked from transmitting on the medium. 3.The method of claim 1, further comprising waiting, by the firsttransmitter, for an opportunity window time period to expire.
 4. Themethod of claim 1, further comprising determining whether transmittingdata at the second power level may interfere with reception of a seconddata transmission.
 5. The method of claim 4, wherein determining whethertransmitting data at the second power level may interfere with receptionof a second data transmission comprises estimating a distance between asecond receiver and the first transmitter based upon a drop in powerfrom a ready to send packet transmitted by the second receiver.
 6. Themethod of claim 4, wherein determining whether transmitting data at thesecond power level may interfere with reception of a second datatransmission comprises estimating a power attenuation between a secondreceiver and the first transmitter based upon a drop in power from aready to send packet transmitted by the second receiver.
 7. The methodof claim 4, wherein determining whether transmitting data at the secondpower level may interfere with reception of a second data transmissioncomprises estimating a third power level that is a power level totransmit the first data transmission that avoids interfering with thesecond data transmission.
 8. The method of claim 7, wherein estimating athird power level that is a power level to transmit the first datatransmission that avoids interfering with the second data transmissioncomprises estimating the third power level as the maximum power levelfor transmitting the first data transmission that avoids interferingwith the second data transmission.
 9. The method of claim 7, whereindetermining whether transmitting data at the second power level mayinterfere with reception of a second data transmission comprisescomparing the third power level with a fourth power level, wherein thefourth power level is a power level that supports a quality of servicefor the first data transmission.
 10. The method of claim 1, whereintransmitting, by the first transmitter, the first data transmission atthe second power level comprises transmitting the first datatransmission at a fourth power level determined to provide quality ofservice for the first data transmission by the first transmitter. 11.The method of claim 1, wherein transmitting the first data transmissionat a fourth power level determined to provide quality of service for thefirst data transmission by the first transmitter comprises transmittingthe first data transmission at the fourth power level, wherein thefourth power level is a minimum power level that supports a quality ofservice for the first data transmission.
 12. An apparatus to enablecoexistence of high-density and low-density transmissions on a medium,the apparatus comprising: a transmitter to transmit on the mediumcomprising a transmit power control to adjust a transmission power topower levels; a memory comprising a buffer for storing a networkallocation value and a buffer for storing a device associated with thenetwork allocation value; and logic to determine whether a value of anetwork allocation vector indicates that the apparatus is blocked fromtransmitting on the medium; to transmit a first ready to send packet ata first power level in response to determining that the apparatus is notblocked from transmitting on the medium; to receive a second clear tosend packet; and to transmit a first data transmission at a second powerlevel, the second power level being less than the first power level. 13.The apparatus of claim 12, wherein the logic further comprises logic toa first clear to send packet at a first power level in response todetermining that the first transmitter is not blocked from transmittingon the medium.
 14. The apparatus of claim 12, wherein the logic furthercomprises logic to wait for an opportunity window time period to expire.15. The apparatus of claim 12, wherein the logic further comprises logicto determine whether transmitting data at the second power level mayinterfere with reception of a second data transmission.
 16. Theapparatus of claim 12, wherein the logic to determine whethertransmitting data at the second power level may interfere with receptionof a second data transmission comprises logic to estimate a distancebetween a second receiver and the first transmitter based upon a drop inpower from a ready to send packet transmitted by the second receiver.17. A computer program product to enable coexistence of high-density andlow-density transmissions, the computer program product comprising: acomputer useable storage medium having a computer useable program codeembodied therewith, the computer useable program code comprising:computer useable program code configured to perform operations, theoperations comprising: determining, by a first transmitter, whether avalue of a network allocation vector maintained by the first transmitterindicates that the first transmitter is blocked from transmitting on amedium; transmitting, by the first transmitter, a first ready to sendpacket at a first power level in response to determining that the firsttransmitter is not blocked from transmitting on the medium; receiving,by the first transmitter, a second clear to send packet; andtransmitting, by the first transmitter, a first data transmission at asecond power level, the second power level being less than the firstpower level.
 18. The computer program product of claim 17, wherein theoperations further comprise transmitting, by the first transmitter, afirst clear to send packet at a first power level in response todetermining that the first transmitter is not blocked from transmittingon the medium.
 19. The computer program product of claim 17, wherein theoperations further comprise determining whether transmitting data at thesecond power level may interfere with reception of a second datatransmission.
 20. The computer program product of claim 17, herein theoperations further comprise waiting, by the first transmitter, for anopportunity window time period to expire.